The invention relates generally to D.C. voltage power supply devices and particularly to a power supply device for high voltage D.C electrodes in an electrostatic system for the prevention of the formation of ink mist in a high speed rotary printing machine.
High voltage D.C. power supply systems are known and in use in similar applications where it is intended to prevent the ambient atmosphere in the printing press room from being polluted by the micro-fine ink mist which is generated by the ink rollers of the printing machine. In one of the best known applications electrodes are installed parallel to the ink rollers of the printing machine and these electrodes are connected to the high voltage D.C. output of the power supply device for electrostatically emitting streams of ionized air against the grounded rollers whereby the micro-fine ink mist particles are prevented from flying off the surface of the rollers and from floating freely in the pressroom atmosphere. In another application of high voltage D.C. for the electrostatic elimination of ink mist, very thin wires are strung parallel of the nips of the ink rollers. These systems and their high voltage D.C. power supply diagrams are shown in the U.S. Pat. Nos. 3,515,064 and 3,011,435. Protecting both the power supply device and the installations in the printing machines against faults or shorts had been provided in the form of fuses and/or electro-mechanical circuit breakers combined with a signal light. Faults can occur in many ways during the operation of the printing machine causing abnormally high currents, such as by electrodes getting dirty, by electrodes being coated with printing ink; by electrodes breaking, arcing or by foreign matter such as paper shreds getting into and between the electrodes and the rollers causing shorts of the high voltage. When such faults occurred, the prior art safety devices turned the power supply off. Since a plurality of other signal lights of all kinds are installed on the printing machines and on the related individual units present in the pressroom, the fault indicating light on the D.C. power supply cabinet of the prior art devices is not always immediately noticed, if at all, resulting in soiling of the machine and in polluting of the air in the pressroom. Another high voltage D.C. supply systems known from the U.S. Pat. No. 3,295,441 provides switching circuits for switching the power supply on after a fault had occurred a certain limited number of "off-on" cycles. No provision has been made in the prior art for alerting effectively the pressroom personnel so that the fault could be corrected.
All known systems comprise electro-mechanical means such as relays, contactors and switches, which are inherently subject to wear, mechanical failures and to a relative delay of action. These prior art systems also do not keep giving efficient alerting signals as long as the fault prevails, and keep probing the fault and re-energizing the system automatically until the fault has been removed, without being in danger of burning out component parts.
The problems which became known by practicing the prior art, concern mainly the elimination of all mechanically movable electrical elements, the lack of an effectful alarming system for alerting the operating personnel about the actual condition of the power system and automatically re-energizing the system after a fault has been cleared away. These problems are solved by the present invention.
This application is copending with its companion case "Printing Machine High Voltage Power System" invented by Huffsmith and assigned to the assignee of the present invention being application Ser. No. 547,870, filed Feb. 7, 1975.